In the past decade, liberals have avoided inconvenient truths about the issue.

The myth, which liberals like myself find tempting, is that only the right has changed. In June 2015, we tell ourselves, Donald Trump rode down his golden escalator and pretty soon nativism, long a feature of conservative politics, had engulfed it. But that’s not the full story. If the right has grown more nationalistic, the left has grown less so. A decade ago, liberals publicly questioned immigration in ways that would shock many progressives today.

In 2005, a left-leaning blogger wrote, “Illegal immigration wreaks havoc economically, socially, and culturally; makes a mockery of the rule of law; and is disgraceful just on basic fairness grounds alone.” In 2006, a liberal columnist wrote that “immigration reduces the wages of domestic workers who compete with immigrants” and that “the fiscal burden of low-wage immigrants is also pretty clear.” His conclusion: “We’ll need to reduce the inflow of low-skill immigrants.” That same year, a Democratic senator wrote, “When I see Mexican flags waved at proimmigration demonstrations, I sometimes feel a flush of patriotic resentment. When I’m forced to use a translator to communicate with the guy fixing my car, I feel a certain frustration.”

The blogger was Glenn Greenwald. The columnist was Paul Krugman. The senator was Barack Obama.

Prominent liberals didn’t oppose immigration a decade ago. Most acknowledged its benefits to America’s economy and culture. They supported a path to citizenship for the undocumented. Still, they routinely asserted that low-skilled immigrants depressed the wages of low-skilled American workers and strained America’s welfare state. And they were far more likely than liberals today are to acknowledge that, as Krugman put it, “immigration is an intensely painful topic … because it places basic principles in conflict.”

Today, little of that ambivalence remains. In 2008, the Democratic platform called undocumented immigrants “our neighbors.” But it also warned, “We cannot continue to allow people to enter the United States undetected, undocumented, and unchecked,” adding that “those who enter our country’s borders illegally, and those who employ them, disrespect the rule of the law.” By 2016, such language was gone. The party’s platform described America’s immigration system as a problem, but not illegal immigration itself. And it focused almost entirely on the forms of immigration enforcement that Democrats opposed. In its immigration section, the 2008 platform referred three times to people entering the country “illegally.” The immigration section of the 2016 platform didn’t use the word illegal, or any variation of it, at all.

“A decade or two ago,” says Jason Furman, a former chairman of President Obama’s Council of Economic Advisers, “Democrats were divided on immigration. Now everyone agrees and is passionate and thinks very little about any potential downsides.” How did this come to be?

There are several explanations for liberals’ shift. The first is that they have changed because the reality on the ground has changed, particularly as regards illegal immigration. In the two decades preceding 2008, the United States experienced sharp growth in its undocumented population. Since then, the numbers have leveled off.

But this alone doesn’t explain the transformation. The number of undocumented people in the United States hasn’t gone down significantly, after all; it’s stayed roughly the same. So the economic concerns that Krugman raised a decade ago remain relevant today.

A larger explanation is political. Between 2008 and 2016, Democrats became more and more confident that the country’s growing Latino population gave the party an electoral edge. To win the presidency, Democrats convinced themselves, they didn’t need to reassure white people skeptical of immigration so long as they turned out their Latino base. “The fastest-growing sector of the American electorate stampeded toward the Democrats this November,” Salon declared after Obama’s 2008 win. “If that pattern continues, the GOP is doomed to 40 years of wandering in a desert.”

As the Democrats grew more reliant on Latino votes, they were more influenced by pro-immigrant activism. While Obama was running for reelection, immigrants’-rights advocates launched protests against the administration’s deportation practices; these protests culminated, in June 2012, in a sit-in at an Obama campaign office in Denver. Ten days later, the administration announced that it would defer the deportation of undocumented immigrants who had arrived in the U.S. before the age of 16 and met various other criteria. Obama, The New York Times noted, “was facing growing pressure from Latino leaders and Democrats who warned that because of his harsh immigration enforcement, his support was lagging among Latinos who could be crucial voters in his race for re-election.”

Alongside pressure from pro-immigrant activists came pressure from corporate America, especially the Democrat-aligned tech industry, which uses the H-1B visa program to import workers. In 2010, New York Mayor Michael Bloomberg, along with the CEOs of companies including Hewlett-Packard, Boeing, Disney, and News Corporation, formed New American Economy to advocate for business-friendly immigration policies. Three years later, Mark Zuckerberg and Bill Gates helped found FWD.us to promote a similar agenda.

This combination of Latino and corporate activism made it perilous for Democrats to discuss immigration’s costs, as Bernie Sanders learned the hard way. In July 2015, two months after officially announcing his candidacy for president, Sanders was interviewed by Ezra Klein, the editor in chief of Vox. Klein asked whether, in order to fight global poverty, the U.S. should consider “sharply raising the level of immigration we permit, even up to a level of open borders.” Sanders reacted with horror. “That’s a Koch brothers proposal,” he scoffed. He went on to insist that “right-wing people in this country would love … an open-border policy. Bring in all kinds of people, work for $2 or $3 an hour, that would be great for them. I don’t believe in that. I think we have to raise wages in this country.”

Sanders came under immediate attack. Vox’s Dylan Matthews declared that his “fear of immigrant labor is ugly—and wrongheaded.” The president of FWD.us accused Sanders of “the sort of backward-looking thinking that progressives have rightly moved away from in the past years.” ThinkProgress published a blog post titled “Why Immigration Is the Hole in Bernie Sanders’ Progressive Agenda.” The senator, it argued, was supporting “the idea that immigrants coming to the U.S. are taking jobs and hurting the economy, a theory that has been proven incorrect.”

Sanders stopped emphasizing immigration’s costs. By January 2016, FWD.us’s policy director noted with satisfaction that he had “evolved on this issue.”

But has the claim that “immigrants coming to the U.S. are taking jobs” actually been proved “incorrect”? A decade ago, liberals weren’t so sure. In 2006, Krugman wrote that America was experiencing “large increases in the number of low-skill workers relative to other inputs into production, so it’s inevitable that this means a fall in wages.”

It’s hard to imagine a prominent liberal columnist writing that sentence today. To the contrary, progressive commentators now routinely claim that there’s a near-consensus among economists on immigration’s benefits.

There isn’t. According to a comprehensive new report by the National Academies of Sciences, Engineering, and Medicine, “Groups comparable to … immigrants in terms of their skill may experience a wage reduction as a result of immigration-induced increases in labor supply.” But academics sometimes de-emphasize this wage reduction because, like liberal journalists and politicians, they face pressures to support immigration.

Many of the immigration scholars regularly cited in the press have worked for, or received funding from, pro-immigration businesses and associations. Consider, for instance, Giovanni Peri, an economist at UC Davis whose name pops up a lot in liberal commentary on the virtues of immigration. A 2015 New York Times Magazine essay titled “Debunking the Myth of the Job-Stealing Immigrant” declared that Peri, whom it called the “leading scholar” on how nations respond to immigration, had “shown that immigrants tend to complement—rather than compete against—the existing work force.” Peri is indeed a respected scholar. But Microsoft has funded some of his research into high-skilled immigration. And New American Economy paid to help him turn his research into a 2014 policy paper decrying limitations on the H-1B visa program. Such grants are more likely the result of his scholarship than their cause. Still, the prevalence of corporate funding can subtly influence which questions economists ask, and which ones they don’t. (Peri says grants like those from Microsoft and New American Economy are neither large nor crucial to his work, and that “they don’t determine … the direction of my academic research.”)

Academics face cultural pressures too. In his book Exodus, Paul Collier, an economist at the University of Oxford, claims that in their “desperate [desire] not to give succor” to nativist bigots, “social scientists have strained every muscle to show that migration is good for everyone.” George Borjas of Harvard argues that since he began studying immigration in the 1980s, his fellow economists have grown far less tolerant of research that emphasizes its costs. There is, he told me, “a lot of self-censorship among young social scientists.” Because Borjas is an immigration skeptic, some might discount his perspective. But when I asked Donald Davis, a Columbia University economist who takes a more favorable view of immigration’s economic impact, about Borjas’s claim, he made a similar point. “George and I come out on different sides of policy on immigration,” Davis said, “but I agree that there are aspects of discussion in academia that don’t get sort of full view if you come to the wrong conclusion.”

None of this means that liberals should oppose immigration. Entry to the United States is, for starters, a boon to immigrants and to the family members back home to whom they send money. It should be valued on these moral grounds alone. But immigration benefits the economy, too. Because immigrants are more likely than native-born Americans to be of working age, they improve the ratio of workers to retirees, which helps keep programs like Social Security and Medicare solvent. Immigration has also been found to boost productivity, and the National Academies report finds that “natives’ incomes rise in aggregate as a result of immigration.”

The problem is that, although economists differ about the extent of the damage, immigration hurts the Americans with whom immigrants compete. And since more than a quarter of America’s recent immigrants lack even a high-school diploma or its equivalent, immigration particularly hurts the least-educated native workers, the very people who are already struggling the most. America’s immigration system, in other words, pits two of the groups liberals care about most—the native-born poor and the immigrant poor—against each other.

One way of mitigating this problem would be to scrap the current system, which allows immigrants living in the U.S. to bring certain close relatives to the country, in favor of what Donald Trump in February called a “merit based” approach that prioritizes highly skilled and educated workers. The problem with this idea, from a liberal perspective, is its cruelty. It denies many immigrants who are already here the ability to reunite with their loved ones. And it flouts the country’s best traditions. Would we remove from the Statue of Liberty the poem welcoming the “poor,” the “wretched,” and the “homeless”?

A better answer is to take some of the windfall that immigration brings to wealthier Americans and give it to those poorer Americans whom immigration harms. Borjas has suggested taxing the high-tech, agricultural, and service-sector companies that profit from cheap immigrant labor and using the money to compensate those Americans who are displaced by it.

Unfortunately, while admitting poor immigrants makes redistributing wealth more necessary, it also makes it harder, at least in the short term. By some estimates, immigrants, who are poorer on average than native-born Americans and have larger families, receive more in government services than they pay in taxes. According to the National Academies report, immigrant-headed families with children are 15 percentage points more likely to rely on food assistance, and 12 points more likely to rely on Medicaid, than other families with children. In the long term, the United States will likely recoup much if not all of the money it spends on educating and caring for the children of immigrants. But in the meantime, these costs strain the very welfare state that liberals want to expand in order to help those native-born Americans with whom immigrants compete.

What’s more, studies by the Harvard political scientist Robert Putnam and others suggest that greater diversity makes Americans less charitable and less willing to redistribute wealth. People tend to be less generous when large segments of society don’t look or talk like them. Surprisingly, Putnam’s research suggests that greater diversity doesn’t reduce trust and cooperation just among people of different races or ethnicities—it also reduces trust and cooperation among people of the same race and ethnicity.

Trump appears to sense this. His implicit message during the campaign was that if the government kept out Mexicans and Muslims, white, Christian Americans would not only grow richer and safer, they would also regain the sense of community that they identified with a bygone age. “At the bedrock of our politics will be a total allegiance to the United States of America,” he declared in his inaugural address, “and through our loyalty to our country, we will rediscover our loyalty to each other.”

Liberals must take seriously Americans’ yearning for social cohesion. To promote both mass immigration and greater economic redistribution, they must convince more native-born white Americans that immigrants will not weaken the bonds of national identity. This means dusting off a concept many on the left currently hate: assimilation.

Promoting assimilation need not mean expecting immigrants to abandon their culture. But it does mean breaking down the barriers that segregate them from the native-born. And it means celebrating America’s diversity less, and its unity more.

Writing last year in American Sociological Review, Ariela Schachter, a sociology professor at Washington University in St. Louis, examined the factors that influence how native-born whites view immigrants. Foremost among them is an immigrant’s legal status. Given that natives often assume Latinos are undocumented even when they aren’t, it follows that illegal immigration indirectly undermines the status of those Latinos who live in the U.S. legally. That’s why conservatives rail against government benefits for undocumented immigrants (even though the undocumented are already barred from receiving many of those benefits): They know Americans will be more reluctant to support government programs if they believe those programs to be benefiting people who have entered the country illegally.

Liberal immigration policy must work to ensure that immigrants do not occupy a separate legal caste. This means opposing the guest-worker programs—beloved by many Democrat-friendly tech companies, among other employers—that require immigrants to work in a particular job to remain in the U.S. Some scholars believe such programs drive down wages; they certainly inhibit assimilation. And, as Schachter’s research suggests, strengthening the bonds of identity between natives and immigrants is harder when natives and immigrants are not equal under the law.

The next Democratic presidential candidate should say again and again that because Americans are one people, who must abide by one law, his or her goal is to reduce America’s undocumented population to zero. For liberals, the easy part of fulfilling that pledge is supporting a path to citizenship for the undocumented who have put down roots in the United States. The hard part, which Hillary Clinton largely ignored in her 2016 presidential run, is backing tough immigration enforcement so that path to citizenship doesn’t become a magnet that entices more immigrants to enter the U.S. illegally.

Enforcement need not mean tearing apart families, as Trump is doing with gusto. Liberals can propose that the government deal harshly not with the undocumented themselves but with their employers. Trump’s brutal policies already appear to be slowing illegal immigration. But making sure companies follow the law and verify the legal status of their employees would curtail it too: Migrants would presumably be less likely to come to the U.S. if they know they won’t be able to find work.

Schachter’s research also shows that native-born whites feel a greater affinity toward immigrants who speak fluent English. That’s particularly significant because, according to the National Academies report, newer immigrants are learning English more slowly than their predecessors did. During the campaign, Clinton proposed increasing funding for adult English-language education. But she rarely talked about it. In fact, she ran an ad attacking Trump for saying, among other things, “This is a country where we speak English, not Spanish.” The immigration section of her website showed her surrounded by Spanish-language signs.

Democrats should put immigrants’ learning English at the center of their immigration agenda. If more immigrants speak English fluently, native-born whites may well feel a stronger connection to them, and be more likely to support government policies that help them. Promoting English will also give Democrats a greater chance of attracting those native-born whites who consider growing diversity a threat. According to a preelection study by Adam Bonica, a Stanford political scientist, the single best predictor of whether a voter supported Trump was whether he or she agreed with the statement “People living in the U.S. should follow American customs and traditions.”

In her 2005 book, The Authoritarian Dynamic, which has been heralded for identifying the forces that powered Trump’s campaign, Karen Stenner, then a professor of politics at Princeton, wrote:

"Exposure to difference, talking about difference, and applauding difference—the hallmarks of liberal democracy—are the surest ways to aggravate those who are innately intolerant, and to guarantee the increased expression of their predispositions in manifestly intolerant attitudes and behaviors. Paradoxically, then, it would seem that we can best limit intolerance of difference by parading, talking about, and applauding our sameness."

The next Democratic presidential nominee should commit those words to memory. There’s a reason Barack Obama’s declaration at the 2004 Democratic National Convention that “there is not a liberal America and a conservative America … There is not a black America and white America and Latino America and Asian America; there’s the United States of America” is among his most famous lines. Americans know that liberals celebrate diversity. They’re less sure that liberals celebrate unity. And Obama’s ability to effectively do the latter probably contributed to the fact that he—a black man with a Muslim-sounding name—twice won a higher percentage of the white vote than did Hillary Clinton.

In 2014, the University of California listed melting pot as a term it considered a “microaggression.” What if Hillary Clinton had traveled to one of its campuses and called that absurd? What if she had challenged elite universities to celebrate not merely multiculturalism and globalization but Americanness? What if she had said more boldly that the slowing rate of English-language acquisition was a problem she was determined to solve? What if she had acknowledged the challenges that mass immigration brings, and then insisted that Americans could overcome those challenges by focusing not on what makes them different but on what makes them the same?

Some on the left would have howled. But I suspect that Clinton would be president today.

In the past decade, liberals have avoided inconvenient truths about the issue.

The myth, which liberals like myself find tempting, is that only the right has changed. In June 2015, we tell ourselves, Donald Trump rode down his golden escalator and pretty soon nativism, long a feature of conservative politics, had engulfed it. But that’s not the full story. If the right has grown more nationalistic, the left has grown less so. A decade ago, liberals publicly questioned immigration in ways that would shock many progressives today.

In 2005, a left-leaning blogger wrote, “Illegal immigration wreaks havoc economically, socially, and culturally; makes a mockery of the rule of law; and is disgraceful just on basic fairness grounds alone.” In 2006, a liberal columnist wrote that “immigration reduces the wages of domestic workers who compete with immigrants” and that “the fiscal burden of low-wage immigrants is also pretty clear.” His conclusion: “We’ll need to reduce the inflow of low-skill immigrants.” That same year, a Democratic senator wrote, “When I see Mexican flags waved at proimmigration demonstrations, I sometimes feel a flush of patriotic resentment. When I’m forced to use a translator to communicate with the guy fixing my car, I feel a certain frustration.”

The blogger was Glenn Greenwald. The columnist was Paul Krugman. The senator was Barack Obama.

Prominent liberals didn’t oppose immigration a decade ago. Most acknowledged its benefits to America’s economy and culture. They supported a path to citizenship for the undocumented. Still, they routinely asserted that low-skilled immigrants depressed the wages of low-skilled American workers and strained America’s welfare state. And they were far more likely than liberals today are to acknowledge that, as Krugman put it, “immigration is an intensely painful topic … because it places basic principles in conflict.”

Today, little of that ambivalence remains. In 2008, the Democratic platform called undocumented immigrants “our neighbors.” But it also warned, “We cannot continue to allow people to enter the United States undetected, undocumented, and unchecked,” adding that “those who enter our country’s borders illegally, and those who employ them, disrespect the rule of the law.” By 2016, such language was gone. The party’s platform described America’s immigration system as a problem, but not illegal immigration itself. And it focused almost entirely on the forms of immigration enforcement that Democrats opposed. In its immigration section, the 2008 platform referred three times to people entering the country “illegally.” The immigration section of the 2016 platform didn’t use the word illegal, or any variation of it, at all.

“A decade or two ago,” says Jason Furman, a former chairman of President Obama’s Council of Economic Advisers, “Democrats were divided on immigration. Now everyone agrees and is passionate and thinks very little about any potential downsides.” How did this come to be?

There are several explanations for liberals’ shift. The first is that they have changed because the reality on the ground has changed, particularly as regards illegal immigration. In the two decades preceding 2008, the United States experienced sharp growth in its undocumented population. Since then, the numbers have leveled off.

But this alone doesn’t explain the transformation. The number of undocumented people in the United States hasn’t gone down significantly, after all; it’s stayed roughly the same. So the economic concerns that Krugman raised a decade ago remain relevant today.

A larger explanation is political. Between 2008 and 2016, Democrats became more and more confident that the country’s growing Latino population gave the party an electoral edge. To win the presidency, Democrats convinced themselves, they didn’t need to reassure white people skeptical of immigration so long as they turned out their Latino base. “The fastest-growing sector of the American electorate stampeded toward the Democrats this November,” Salon declared after Obama’s 2008 win. “If that pattern continues, the GOP is doomed to 40 years of wandering in a desert.”

As the Democrats grew more reliant on Latino votes, they were more influenced by pro-immigrant activism. While Obama was running for reelection, immigrants’-rights advocates launched protests against the administration’s deportation practices; these protests culminated, in June 2012, in a sit-in at an Obama campaign office in Denver. Ten days later, the administration announced that it would defer the deportation of undocumented immigrants who had arrived in the U.S. before the age of 16 and met various other criteria. Obama, The New York Times noted, “was facing growing pressure from Latino leaders and Democrats who warned that because of his harsh immigration enforcement, his support was lagging among Latinos who could be crucial voters in his race for re-election.”

Alongside pressure from pro-immigrant activists came pressure from corporate America, especially the Democrat-aligned tech industry, which uses the H-1B visa program to import workers. In 2010, New York Mayor Michael Bloomberg, along with the CEOs of companies including Hewlett-Packard, Boeing, Disney, and News Corporation, formed New American Economy to advocate for business-friendly immigration policies. Three years later, Mark Zuckerberg and Bill Gates helped found FWD.us to promote a similar agenda.

This combination of Latino and corporate activism made it perilous for Democrats to discuss immigration’s costs, as Bernie Sanders learned the hard way. In July 2015, two months after officially announcing his candidacy for president, Sanders was interviewed by Ezra Klein, the editor in chief of Vox. Klein asked whether, in order to fight global poverty, the U.S. should consider “sharply raising the level of immigration we permit, even up to a level of open borders.” Sanders reacted with horror. “That’s a Koch brothers proposal,” he scoffed. He went on to insist that “right-wing people in this country would love … an open-border policy. Bring in all kinds of people, work for $2 or $3 an hour, that would be great for them. I don’t believe in that. I think we have to raise wages in this country.”

Sanders came under immediate attack. Vox’s Dylan Matthews declared that his “fear of immigrant labor is ugly—and wrongheaded.” The president of FWD.us accused Sanders of “the sort of backward-looking thinking that progressives have rightly moved away from in the past years.” ThinkProgress published a blog post titled “Why Immigration Is the Hole in Bernie Sanders’ Progressive Agenda.” The senator, it argued, was supporting “the idea that immigrants coming to the U.S. are taking jobs and hurting the economy, a theory that has been proven incorrect.”

Sanders stopped emphasizing immigration’s costs. By January 2016, FWD.us’s policy director noted with satisfaction that he had “evolved on this issue.”

But has the claim that “immigrants coming to the U.S. are taking jobs” actually been proved “incorrect”? A decade ago, liberals weren’t so sure. In 2006, Krugman wrote that America was experiencing “large increases in the number of low-skill workers relative to other inputs into production, so it’s inevitable that this means a fall in wages.”

It’s hard to imagine a prominent liberal columnist writing that sentence today. To the contrary, progressive commentators now routinely claim that there’s a near-consensus among economists on immigration’s benefits.

There isn’t. According to a comprehensive new report by the National Academies of Sciences, Engineering, and Medicine, “Groups comparable to … immigrants in terms of their skill may experience a wage reduction as a result of immigration-induced increases in labor supply.” But academics sometimes de-emphasize this wage reduction because, like liberal journalists and politicians, they face pressures to support immigration.

Many of the immigration scholars regularly cited in the press have worked for, or received funding from, pro-immigration businesses and associations. Consider, for instance, Giovanni Peri, an economist at UC Davis whose name pops up a lot in liberal commentary on the virtues of immigration. A 2015 New York Times Magazine essay titled “Debunking the Myth of the Job-Stealing Immigrant” declared that Peri, whom it called the “leading scholar” on how nations respond to immigration, had “shown that immigrants tend to complement—rather than compete against—the existing work force.” Peri is indeed a respected scholar. But Microsoft has funded some of his research into high-skilled immigration. And New American Economy paid to help him turn his research into a 2014 policy paper decrying limitations on the H-1B visa program. Such grants are more likely the result of his scholarship than their cause. Still, the prevalence of corporate funding can subtly influence which questions economists ask, and which ones they don’t. (Peri says grants like those from Microsoft and New American Economy are neither large nor crucial to his work, and that “they don’t determine … the direction of my academic research.”)

Academics face cultural pressures too. In his book Exodus, Paul Collier, an economist at the University of Oxford, claims that in their “desperate [desire] not to give succor” to nativist bigots, “social scientists have strained every muscle to show that migration is good for everyone.” George Borjas of Harvard argues that since he began studying immigration in the 1980s, his fellow economists have grown far less tolerant of research that emphasizes its costs. There is, he told me, “a lot of self-censorship among young social scientists.” Because Borjas is an immigration skeptic, some might discount his perspective. But when I asked Donald Davis, a Columbia University economist who takes a more favorable view of immigration’s economic impact, about Borjas’s claim, he made a similar point. “George and I come out on different sides of policy on immigration,” Davis said, “but I agree that there are aspects of discussion in academia that don’t get sort of full view if you come to the wrong conclusion.”

None of this means that liberals should oppose immigration. Entry to the United States is, for starters, a boon to immigrants and to the family members back home to whom they send money. It should be valued on these moral grounds alone. But immigration benefits the economy, too. Because immigrants are more likely than native-born Americans to be of working age, they improve the ratio of workers to retirees, which helps keep programs like Social Security and Medicare solvent. Immigration has also been found to boost productivity, and the National Academies report finds that “natives’ incomes rise in aggregate as a result of immigration.”

The problem is that, although economists differ about the extent of the damage, immigration hurts the Americans with whom immigrants compete. And since more than a quarter of America’s recent immigrants lack even a high-school diploma or its equivalent, immigration particularly hurts the least-educated native workers, the very people who are already struggling the most. America’s immigration system, in other words, pits two of the groups liberals care about most—the native-born poor and the immigrant poor—against each other.

One way of mitigating this problem would be to scrap the current system, which allows immigrants living in the U.S. to bring certain close relatives to the country, in favor of what Donald Trump in February called a “merit based” approach that prioritizes highly skilled and educated workers. The problem with this idea, from a liberal perspective, is its cruelty. It denies many immigrants who are already here the ability to reunite with their loved ones. And it flouts the country’s best traditions. Would we remove from the Statue of Liberty the poem welcoming the “poor,” the “wretched,” and the “homeless”?

A better answer is to take some of the windfall that immigration brings to wealthier Americans and give it to those poorer Americans whom immigration harms. Borjas has suggested taxing the high-tech, agricultural, and service-sector companies that profit from cheap immigrant labor and using the money to compensate those Americans who are displaced by it.

Unfortunately, while admitting poor immigrants makes redistributing wealth more necessary, it also makes it harder, at least in the short term. By some estimates, immigrants, who are poorer on average than native-born Americans and have larger families, receive more in government services than they pay in taxes. According to the National Academies report, immigrant-headed families with children are 15 percentage points more likely to rely on food assistance, and 12 points more likely to rely on Medicaid, than other families with children. In the long term, the United States will likely recoup much if not all of the money it spends on educating and caring for the children of immigrants. But in the meantime, these costs strain the very welfare state that liberals want to expand in order to help those native-born Americans with whom immigrants compete.

What’s more, studies by the Harvard political scientist Robert Putnam and others suggest that greater diversity makes Americans less charitable and less willing to redistribute wealth. People tend to be less generous when large segments of society don’t look or talk like them. Surprisingly, Putnam’s research suggests that greater diversity doesn’t reduce trust and cooperation just among people of different races or ethnicities—it also reduces trust and cooperation among people of the same race and ethnicity.

Trump appears to sense this. His implicit message during the campaign was that if the government kept out Mexicans and Muslims, white, Christian Americans would not only grow richer and safer, they would also regain the sense of community that they identified with a bygone age. “At the bedrock of our politics will be a total allegiance to the United States of America,” he declared in his inaugural address, “and through our loyalty to our country, we will rediscover our loyalty to each other.”

Liberals must take seriously Americans’ yearning for social cohesion. To promote both mass immigration and greater economic redistribution, they must convince more native-born white Americans that immigrants will not weaken the bonds of national identity. This means dusting off a concept many on the left currently hate: assimilation.

Promoting assimilation need not mean expecting immigrants to abandon their culture. But it does mean breaking down the barriers that segregate them from the native-born. And it means celebrating America’s diversity less, and its unity more.

Writing last year in American Sociological Review, Ariela Schachter, a sociology professor at Washington University in St. Louis, examined the factors that influence how native-born whites view immigrants. Foremost among them is an immigrant’s legal status. Given that natives often assume Latinos are undocumented even when they aren’t, it follows that illegal immigration indirectly undermines the status of those Latinos who live in the U.S. legally. That’s why conservatives rail against government benefits for undocumented immigrants (even though the undocumented are already barred from receiving many of those benefits): They know Americans will be more reluctant to support government programs if they believe those programs to be benefiting people who have entered the country illegally.

Liberal immigration policy must work to ensure that immigrants do not occupy a separate legal caste. This means opposing the guest-worker programs—beloved by many Democrat-friendly tech companies, among other employers—that require immigrants to work in a particular job to remain in the U.S. Some scholars believe such programs drive down wages; they certainly inhibit assimilation. And, as Schachter’s research suggests, strengthening the bonds of identity between natives and immigrants is harder when natives and immigrants are not equal under the law.

The next Democratic presidential candidate should say again and again that because Americans are one people, who must abide by one law, his or her goal is to reduce America’s undocumented population to zero. For liberals, the easy part of fulfilling that pledge is supporting a path to citizenship for the undocumented who have put down roots in the United States. The hard part, which Hillary Clinton largely ignored in her 2016 presidential run, is backing tough immigration enforcement so that path to citizenship doesn’t become a magnet that entices more immigrants to enter the U.S. illegally.

Enforcement need not mean tearing apart families, as Trump is doing with gusto. Liberals can propose that the government deal harshly not with the undocumented themselves but with their employers. Trump’s brutal policies already appear to be slowing illegal immigration. But making sure companies follow the law and verify the legal status of their employees would curtail it too: Migrants would presumably be less likely to come to the U.S. if they know they won’t be able to find work.

Schachter’s research also shows that native-born whites feel a greater affinity toward immigrants who speak fluent English. That’s particularly significant because, according to the National Academies report, newer immigrants are learning English more slowly than their predecessors did. During the campaign, Clinton proposed increasing funding for adult English-language education. But she rarely talked about it. In fact, she ran an ad attacking Trump for saying, among other things, “This is a country where we speak English, not Spanish.” The immigration section of her website showed her surrounded by Spanish-language signs.

Democrats should put immigrants’ learning English at the center of their immigration agenda. If more immigrants speak English fluently, native-born whites may well feel a stronger connection to them, and be more likely to support government policies that help them. Promoting English will also give Democrats a greater chance of attracting those native-born whites who consider growing diversity a threat. According to a preelection study by Adam Bonica, a Stanford political scientist, the single best predictor of whether a voter supported Trump was whether he or she agreed with the statement “People living in the U.S. should follow American customs and traditions.”

In her 2005 book, The Authoritarian Dynamic, which has been heralded for identifying the forces that powered Trump’s campaign, Karen Stenner, then a professor of politics at Princeton, wrote:

"Exposure to difference, talking about difference, and applauding difference—the hallmarks of liberal democracy—are the surest ways to aggravate those who are innately intolerant, and to guarantee the increased expression of their predispositions in manifestly intolerant attitudes and behaviors. Paradoxically, then, it would seem that we can best limit intolerance of difference by parading, talking about, and applauding our sameness."

The next Democratic presidential nominee should commit those words to memory. There’s a reason Barack Obama’s declaration at the 2004 Democratic National Convention that “there is not a liberal America and a conservative America … There is not a black America and white America and Latino America and Asian America; there’s the United States of America” is among his most famous lines. Americans know that liberals celebrate diversity. They’re less sure that liberals celebrate unity. And Obama’s ability to effectively do the latter probably contributed to the fact that he—a black man with a Muslim-sounding name—twice won a higher percentage of the white vote than did Hillary Clinton.

In 2014, the University of California listed melting pot as a term it considered a “microaggression.” What if Hillary Clinton had traveled to one of its campuses and called that absurd? What if she had challenged elite universities to celebrate not merely multiculturalism and globalization but Americanness? What if she had said more boldly that the slowing rate of English-language acquisition was a problem she was determined to solve? What if she had acknowledged the challenges that mass immigration brings, and then insisted that Americans could overcome those challenges by focusing not on what makes them different but on what makes them the same?

Some on the left would have howled. But I suspect that Clinton would be president today.